The present invention relates to a semiconductor device of the flat package type. More particularly, it relates to a semiconductor device having an increased number of pins and also to a method of producing the same.
In general, a semiconductor device of the flat package type can be made thinner and with increased number of pins as compared with a semiconductor device of the dual in-line package type. Moreover, the installation of the former on a mounting circuit board (printed circuit board) requires only mounting operations to substantially the same extent as in case of a semiconductor device of the chip carrier package type. Owing to these advantages, its demand is increasing. The semiconductor device of the specified type is usually so constructed that a semiconductor element pellet is fastened on a lead frame obtained by punching and forming a metal sheet and is electrically connected with leads, whereupon the pellet and the connected parts of the leads are encapsulated with a resin (plastics) into the shape of a square (regular square or oblong) and thin-walled package. When the shape of the package in plan is square in this manner, one corner of a package body 1 is removed to form a chamfered portion 2, as illustrated in FIG. 1, and the chamfered portion 2 is utilized as an index for a plurality of pins (leads) 3.
Meanwhile, semiconductor devices in recent years have a tendency toward an increasingly high density of integration and large number of pins. On the other hand, it is sometimes requested to keep the geometry of a package body constant for the reason of design, fabrication or mounting. In such cases, accordingly, the larger number of pins are inevitably coped with by making the pitches of the leads as small as possible and disposing the pins 3 with the perimeter of the four sides of the package body 1 utilized to the utmost.
In the prior art semiconductor device, however, the chamfered portion 2 as the index is formed, and no pin 3 is disposed in this portion. This lowers the degree of utilization of the four perimetric sides of the package body, and forms an obstacle to the increase of the number of pins. Moreover, since no pin is disposed in the chamfered portion 2, it is impossible, particularly on side faces 1a and 1b adjoining the chamfered portion 2, to array the pins symmetrically with respect to the center 0 of the package body 1. This sometimes leads to a demerit in design, fabrication or mounting. Further, as will be described in detail later, since no pin is disposed in the chamfered portion 2, naturally the part of the lead frame corresponding thereto is provided with no lead. For this reason, plastics leak out in the operation of molding with the plastics, resulting in the problem that degradation in the external appearance or chipping of the package is incurred to spoil the marketability of the semiconductor device.